The Vault of Glass is a Vex site where they try to insert themselves into reality. They are literally trying to become a physical law (and don't ask how that works, no one knows). The Oracles are the first manifestation of these "transcended" Vex: they have become a law of reality, but only within the Vault of Glass, as this is the Vex's main "thorn" in the time-space continuum's side.

[quote]Hi again. What are the oracles? They're the only enemy that doesn't have a grimoire card yet. What do we know of them?[/quote] Oracles. They are vex constructs. They are the ones whom decide whether you exist. Once they decide you are marked for the templar to use it's power to negate your existence. They were made by the vex to try an control reality. Did this help. How bout I mentor lmao all the lore questions